Asynchronous machines have long been generally known, for example from WO 98/40958, DE 32 34 673, WO 90/13937 and U.S. Pat. No. 5,838,135 and are used for many different drive and adjusting functions. In that respect one adjusting function is frequently displacement of a part of a machine from an initial position into a predeterminable new target position.
A situation of use, by way of example, is adjustment of the azimuth position in wind power installations. That adjustment of the azimuth position, namely orientation of the pod in the case of horizontal-axis installations, provides that the rotor of the installation can be caused to track the wind in order thus to be able to continuously generate electrical energy.
To implement that wind direction tracking procedure, the pod of such a wind power installation is supported rotatably and is displaced by way of at least one so-called azimuth motor. Such displacement is effected by a procedure whereby for example a drive gear pinion engages into a tooth arrangement at the top of the pylon and displaces the pod with respect to the top of the pylon, by actuation of the motor. The asynchronous machine is stopped when the desired azimuth position is reached.
It will be noted however that the azimuth position does not change upon every minor deviation in the wind direction. As a result, when slight changes in wind direction are involved, that means that the wind involves an inclined afflux flow in relation to the rotor, and that entails a resulting yaw moment about the vertical axis of the wind power installation at the pod. In order that this yaw moment does not result in an unwanted change in the azimuth position, the azimuth motors can be supplied with a direct current in order to produce a suitable braking moment.
Problems however still occur due to the mechanical components employed. Even with the highest degree of accuracy and the utmost care, it is impossible to avoid play between the gear ring at the top of the pylon and the drive pinions. When fluctuating yaw moments occur, that results in a corresponding movement of the pod within the range which that play allows.